1. Field of the Invention
The present invention relates to an imaging apparatus and the processing method thereof.
2. Description of the Related Arts
The following three kinds of driving methods for enlarging a dynamic range of a solid-state imaging apparatus is disclosed in Japanese Patent Application Laid-Open No. 2005-328493. The first kind is such that a carrier overflowed from a photo receiving unit is accumulated in floating diffusion and an added capacitor so as to be turned into a dynamic range expansion signal. The second kind is such that, during a part of the period only within the accumulation period of the photo receiving unit, the overflowed carrier is accumulated so as to be turned into a dynamic range expansion signal. The third kind is such that the signal accumulated in the photo receiving unit as well as the dynamic range expansion signal are added inside a pixel so as to be output.
Japanese Patent Application Laid-Open No. 2005-328493 discloses that the floating diffusion contains a dark impurity region and a PN junction composed of a p-type well, and that a photo diode is an embedded photo diode. However, there is a problem that the floating diffusion is great in dark output due to the generation current in a depletion layer for the photo diode.
Although there is no cause for concern when the accumulation period is short, when the accumulation period is long, a problem occurs that many signals are generated due to dark currents of a floating diffusion region that accumulates the dynamic range expansion signals as well as the added capacitor. This is because the FD and CS units are not the PN junction capacitor of the berried type, and as a result, the dark current is increased, and therefore, they are not suitable as holding units for holding the carrier for a long time. The signal amplitude at the FD (or a vertical signal line) is put on restrictions by a dark current component, and no signal amplitude for the dynamic range expansion signal can be secured.
This problem can be improved to a certain degree by the second kind of the driving method by making the accumulation period of the dynamic range expansion signal short. However, this time, the accumulation period of the photo diode and the accumulation period of the dynamic range expansion signal are deviated from each other, and therefore, there arises a major problem that the synchronicity of the two signals are harmed. Whichever case it may be, in the case of moving image, since the accumulation period is short, no problem is caused, whereas in the case of the still image photographing such as a digital single-lens reflex camera, it is a major problem.
An object of the present invention is to provide an imaging apparatus and its processing method capable of enlarging a dynamic range, while securing synchronicity of the carrier accumulation period of a photoelectric conversion unit and a carrier accumulation unit.